transformer installation and commissioning

An electrical transformer should be inspected for damage before installation. Please be sure to check for any visible damage, loose or broken parts, dirt, or the presence of moisture. If these signs are not visible, then your transformer should be in good conditions and ready to be installed.

There are three basic parts of a transformer:

• an iron core which serves as a magnetic conductor,
• a primary winding or coil of wire and.
• a secondary winding or coil of wire.

The following pre-commissioning tests/checks shall be conducted: Measurement of insulation resistance – Phase to earth, Between phases, across contacts with breaker open. Measurement of capacitance and tanδ of voltage grading capacitors. The grading capacitors are oil filled paper capacitor type

Electrical test recommendations for transformers

A primary part of commissioning a transformer involves testing it after its installation in the field. This amounts to a rigorous examination of the transformer intended to:

1) uncover problem(s), if any, with the transformer’s components, as a transformer is exposed to great stresses on its journey to site and is vulnerable to moisture ingress during installation and other unplanned maladies,
2) validate that the transformer tests the same as it did when last tested at the manufacturer’s facility,
3) establish a baseline with which to compare results of future tests. For many tests, this will be almost essential to diagnose problems effectively in the future.


A generic square placeholder image with rounded corners in a figure.
A generic square placeholder image with rounded corners in a figure.
A generic square placeholder image with rounded corners in a figure.

The electrical tests recommended for commissioning a transformer include:

Transformer turns ratio
Bushing CT ratio
Tan delta/ Power factor/ dissipation factor (50/60 Hz)
NB DFR (narrow band dielectric frequency response), 1 – 500 HZ
Dielectric frequency response (DFR)
Surge arrester loss (Watts) and current
Exciting current
Leakage reactance (short circuit impedance)
Winding resistance
Sweep frequency response analysis (SFRA)
Frequency response of stray losses
Dynamic winding resistance (on-load tap changing transformers)
Core ground
Dielectric breakdown on oil sample

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